The present invention relates to wireless communications, and more particularly to a calibrated DC compensation system for a wireless communication device configured in a zero intermediate frequency (ZIF) architecture that utilizes a DC control loop to enable direct conversion of radio frequency signals to baseband frequency and a calibration procedure that more accurately determines and controls DC voltage levels.
Network communication is a growing area of technology both for business and home applications. A network system enhances communication and provides a suitable environment for enhanced productivity and capabilities both at home and in the workplace. The Internet for example, is a global, mostly wired, communication network that couples devices together on a world-wide basis that enables world-wide communication between any devices coupled to the Internet. The Internet enables access to a plurality of services, such as file sharing, faxing, chat, email and information access via websites to files, libraries, databases, computer programs, etc.
Many businesses and commercial entities include a relatively established and sophisticated network environment for enhanced productivity and communication. For example, Extranets or Intranets provide enhanced yet protected or secure communication to a selected group of people on the Internet. Many small businesses and homes are coupled to the Internet via some variation of local area network (LAN) or the like. It is becoming more advantageous and common for small businesses and home environments to include LAN capabilities to connect to the Internet or to access other services, such as file sharing, printing, faxing, etc. and to further enable communication such as via chat and email services, and the like and to provide access to common databases and libraries, etc. Many such small networks are connected through a set of wires. For example, a network may be established in a small office or home through standard phone wires. Phone wires are already available in each office of a business and in several rooms of a typical home. Technology also exists to establish network communications via power lines which are typically available in every room of a house. Many small offices and homes may alternatively be wired with network wires, such as a twisted-pair telephone wires with corresponding RJ-45 connectors utilized by various Ethernet embodiments.
Wired networks provide a certain level of convenience but have many limitations. Each device coupled to the network must be attached to a corresponding wire through which the network is established. The location of each device, therefore, is limited to enable access to the network wires. Cable management is also a significant issue, since devices must be placed to enable proper routing of wires. It is desired that the wires be conveniently placed and for aesthetic reasons, out of sight. Wires should be located in such a manner as to reduce or eliminate any chance of accidental interference or disconnect or hazards such as tripping. Once wired devices are properly placed, movement of the devices is very limited or otherwise not practical without substantial re-configuration or re-routing of the wires. Maintenance of wired network devices can be inconvenient and often requires that the wires be removed during service and then reconnected properly.
Certain wireless technologies are known, such as infrared technology. Infrared technology works well for certain applications, such as remote control systems or the like. For network applications, infrared technology is a relatively inexpensive option but has certain limitations, including limited bandwidth, range limitations, and line-of-sight issues. Infrared technology has been utilized in certain applications, such as access points (APs) and point to point relay nodes to extend a network down hallways and the like. For example, infrared devices are known for use in hospitals, hotels and other relatively large structures. The APs or nodes, however, are usually fixed and located in such a manner, such as on the ceiling, to avoid potential interference with physical objects. Due to line of sight issues, infrared technology is not particularly convenient for network communications at the end points of the network where human interaction is necessary.
Radio frequency (RF) technology appears to be the technology of choice for establishing a viable wireless local area network (WLAN). RF technology for LAN systems, however, is not particularly optimized for small office or home use. Wireless technology is established for industrial and commercial uses and applications such as courier services, vehicle rentals, warehouse operations and inventories, etc. The wireless embodiments for commercial and industrial applications are too expensive or otherwise specialized and thus are not suited for direct use in the small office or home environment.
The Bluetooth technology is being developed for application in the home or office. Bluetooth technology offers relatively limited bandwidth at very low cost to enable connectivity and network communications between certain communication devices, such as cellular phones, computer systems including notebook, laptop and desktop computers and further including other hand-held devices such as personal digital assistants (PDAs) or the like. The Bluetooth technology, however, has limited bandwidth and therefore relatively low data throughput capability. The consumer market demands higher data throughput and reliability such as is necessary for DVD and other multimedia applications.
The typical environment for a WLAN is very noisy and not optimal for wireless communications. For example, most homes include many electronic devices resulting in an electronically noisy environment that may interfere with WLAN communications, such as microwave ovens, garage door openers, radios, television sets, computer systems, etc. Further, the communication medium between wireless devices constantly changes. For example, most environments or rooms include multiple reflective surfaces creating multipath noise in the wireless environment. Furthermore, movement of items or devices or the like such as hands, bodies, jewelry, mouse pointers, etc. or activation of electronic devices, such as cooling fans or the like, affects the overall wireless communication path and potentially degrades wireless communication performance.
Low cost and low power wireless communication devices for enabling a WLAN system or the like for use at home or in the small business is desirable. It is further desired to provide low cost and low power wireless communication devices for any type of wireless system for any type of application. The system must be relatively robust with significant performance and be capable of significant data throughput.
A calibrated DC compensation system for a wireless communication device configured in a zero intermediate frequency (ZIF) architecture that includes a gain converter and a calibrator that periodically performs a calibration procedure and that programs the gain converter accordingly. The wireless device includes a combiner that combines a DC offset signal from an input signal and that provides an adjusted input signal. The wireless device further includes DC control logic that generates the DC offset signal and gain control logic that attempts to keep the input signal power at a target level. The gain converter converts gain between the gain control logic and the DC control logic based on programmed values.
In a primary signal path of the wireless device, the gain amplifier receives the adjusted input signal and provides an amplified input signal based on a gain adjust signal. The gain control logic includes a gain feedback circuit that receives the amplified input signal, that estimates input signal power and that provides the gain adjust signal in an attempt to maintain the input signal power at the target power level. The DC control logic includes a DC estimator that estimates a DC level in the amplified input signal and that provides a DC estimate signal. The DC control logic also includes a DC amplifier that receives the DC estimate signal and that provides the DC offset signal based on a gain conversion signal. The gain converter receives the gain adjust signal and provides the gain conversion signal to the DC amplifier.
The gain converter may be a lookup table that stores gain conversion values. During operation, the lookup table provides a gain conversion value for each gain step of the gain adjust signal. The calibrator performs the calibration procedure to determine gain values, where each gain value represents the gain of the gain amplifier at each gain step of the gain adjust signal. The calibrator determines the gain conversion values based on the gain values and programs the lookup table. The calibrator may incorporate differences in gain ranges and gain scales between the gain amplifier and the DC amplifier when determining the gain conversion values.
During each calibration procedure, the calibrator controls the gain feedback circuit to apply the gain adjust signal to each gain step, adjusts a DC offset and samples the amplified input signal until the amplified input signal achieves first and second predetermined range values. The calibrator determines first and second DC offset values that correspond to the first and second predetermined range values, respectively. The calibrator determines the gain conversion values using the range values and the DC offset values for each of the gain steps. The first and second predetermined range values may correspond to a predetermined range of the amplified input signal, where the calibrator uses a successive approximation procedure to determine the first and second DC offset values. For example, the predetermined range values may correspond to xc2x175 millivolts (mV) full scale values.
The gain feedback circuit may further include a gain adjust limiter that limits change of the gain adjust signal during operation. The gain adjust limiter may limit the change of the gain adjust signal based on a maximum gain change limit or on one or more gain change limits. A separate gain change limit may be provided for each gain step of the gain adjust signal, or those gain steps that correspond to higher gain levels. The calibrator may use an upper bound method to determine the maximum gain change limit based on the determined gain values and a predetermined linear DC offset change model of the gain amplifier. The calibrator determines a plurality of DC offset values, where each DC offset value corresponds to one of the gain values determined for the gain amplifier. The calibrator determines the gain change limits using the gain values and DC offset values and programs the gain adjust limiter with the resulting gain change limits. During operation, the gain adjust limiter monitors the current level of the gain adjust signal, receives an error signal indicated desired change of the gain adjust signal, retrieves a corresponding gain change limit and limits application of the error signal to change the gain adjust signal based on the retrieved gain change limit.
Alternatively or in addition, the calibrated DC compensation system includes a second lookup table that stores a plurality of DC adjust values, each corresponding to one of the gain steps of the gain adjust signal. In operation, the second lookup table provides a corresponding DC adjust value for each gain step of the gain adjust signal. The calibrator determines the DC adjust values using the first and second DC offset values for each of the gain steps of the gain adjust signal. The DC amplifier provides a gain compensated DC signal to a combiner, which adds a DC adjust value from the second lookup table to the gain compensated DC signal to provide the DC offset signal.
Alternatively, the gain converter may include an adjust memory which includes a plurality of adjust values, each adjust value corresponding to a gain step of the gain adjust signal. The gain converter provides the gain conversion signal to the DC amplifier based on the gain adjust signal and a corresponding adjust value. The calibrator determines a plurality of DC differential values, each DC differential value corresponding to at least one gain step of the gain adjust signal. The calibrator programs the adjust memory based on the DC differential values. The adjust values may incorporate conversion of gain ranges and gain scales between the gain amplifier and the DC amplifier, and may comprise multipliers or additive values.
In a more specific embodiment, the wireless communication device includes a ZIF transceiver and a baseband processor, where the baseband processor includes calibration logic that periodically performs a calibration procedure. The ZIF transceiver includes a radio frequency (RF) mixer circuit that converts an RF signal to a baseband input signal, a combiner that combines a DC offset with the baseband input signal to provide an adjusted baseband input signal, and a baseband amplifier that receives the adjusted baseband input signal and that asserts an amplified input signal based on a gain adjust signal. The baseband processor includes gain control logic, DC control logic, a gain converter and the calibration logic. The gain control logic receives the amplified input signal, estimates input signal power and asserts the gain adjust signal in an attempt to keep the input signal power at a target power level. The DC control logic estimates an amount of DC in the amplified input signal and provides the DC offset in an attempt to reduce DC in the amplified input signal. The gain converter converts gain between the gain control logic and the DC control logic. The calibration logic programs the gain converter with values determined during the calibration procedure.
A method of reducing DC in a wireless ZIF device includes converting a received radio frequency (RF) signal to a baseband signal, combining a DC offset with the baseband signal to achieve an adjusted baseband signal, amplifying the adjusted baseband signal based on a gain signal to achieve an amplified input signal, determining a power level of an input baseband signal from the amplified input signal, controlling the gain signal to achieve a target power level of the input baseband signal, determining a DC level of the amplified input signal, providing a gain conversion signal based on the gain signal, controlling the DC offset based on the gain conversion signal and the determined DC level of the amplified input signal in an attempt to reduce the DC level of the amplified input signal, and periodically performing a calibration procedure to adjust the gain conversion signal.
The calibration procedure may further comprise measuring a gain value for each of a plurality of gain levels of the gain signal, and storing a plurality of gain conversion values. The method may include providing one of the plurality of gain conversion values for each of the plurality of gain levels of the gain signal. The calibration procedure may further include determining a maximum gain change limit, where the method includes limiting change of the gain signal based on a gain level of the gain signal and the maximum gain change limit. The calibration procedure may further include measuring a plurality of DC offset values, each corresponding to one of a plurality of gain levels of the gain signal, determining a plurality of gain change limit values based on the gain values and the DC offset values, and storing the gain change limit values. The method may further include limiting change of the gain signal based on a gain level of the gain signal and a corresponding gain change limit values. The method may further include storing a plurality of DC adjust values and adding a DC adjust value based on a gain level of the gain signal.
The method may further include setting the gain signal to each of a plurality of gain levels, and for each gain level, determining a first DC offset value to achieve a first predetermined range limit of the amplified input signal, and determining a second DC offset value to achieve a second predetermined range limit of the amplified input signal. The determining of the first and second DC offset values may be based on successive approximation.
It is appreciated that removal of the IF portion of a high performance wireless transceiver, with proper DC compensation and DC calibration, results in a relatively high performance, low cost wireless ZIF transceiver with reduced power requirements. The use of a calibrated DC compensation loop interfaced to the gain loop according to embodiments of the present invention achieves these goals. Such capability enables a WLAN system to be designed for use at home or in the small business that is relatively robust and that has significant performance with relatively high data throughput operation.